I have a motor off at the end of my gcode. My carriages will typically descend 5-10mm after it homes and shuts off. In one case though it fell a few inches. I've already tightened the eccentric a little more. Has anyone else experienced this?

This is normal. The weight of the effector and carriages are greater than the magnetic holding force of an unpowered NEMA. It is possible to increase wheel tension to stop falling BUT... this may lead to flat spots on your wheels if they are left in one spot for extended time. I allow the fall on my machines.